Powered gimbal system

ABSTRACT

A gimbal system utilizing two torque motor drives wherein the motors are on the drive axes and whose rotors and cases provide the gimbal structure for increased off boresite capability (look angle), faster response time due to reduced inertia, low swept volume and low cost based on the simplicity of the structure.

This invention was made under contract to the U.S. Air Force.

FIELD OF THE INVENTION

The invention relates to a simplified gimbal system for a platform suchas one which might be used to point an antenna or an optical system in atarget seeking missile system.

BACKGROUND OF THE INVENTION

Gimbal systems for contemporary seeker missile use have progressedbeyond classic two ring gimbal systems. The demands for fast responsetime, wide look angles, low cost, low swept volume and accuracy havebeen met by systems such as the one described in "STABILIZED PLATFORMSYSTEM" U.S. Pat. No. 4,068,538 by Butler et al. and "OBLIQUE AXISSEEKER", patent application Ser. No. 943,598 by Reid, both assigned tothe assignee of the instant invention. Each of these systems hascontributed to the state of the art in terms of operating capabilitiesand low cost implementation. The Butler et al. system, supra, utilizes acomplex of coupling devices and structure to support the platform. Eachof these components contributes off center mass which increases theinertia of the system. The component count is relatively high whichtends to decrease reliability, decrease useable servo system bandwidthand to increase cost of fabrication and assembly. The swept volume ofthis system is very low, however.

The Reid system, supra, employs substantially non-orthogonal axes toaccomplish continuous motor operation without need for motor reversal ina search or sweep mode of operation. However, this system also suffersfrom high inertia due to the geared linkage and, in some configurations,it may be prone to gimbal lock-up within a desired range of "look"angles. The non-orthogonal axes configuration requires a complexmathematical conversion for operating an X/Y axis control fin system.

SUMMARY OF THE INVENTION

These and other problems are resolved by means of the instant inventionwhich employs drive motors on orthogonal axes. The drive motors arecoupled case to case, case to rotor or rotor to rotor to provide twodimensional control of a platform for carrying an antenna, optics or thelike.

It is therefore an object of the invention to provide a driven gimbalsystem with a small swept volume.

It is another object of the invention to provide a driven gimbal systemhaving a low moment of inertia.

It is still another object of the invention to provide a low cost drivengimbal system.

It is yet another object of the invention to provide a driven gimbalsystem which does not exhibit gimbal lock-up when in a boresiteposition.

It is still another object of the invention to provide a highreliability driven gimbal system.

It is again another object of the invention to provide a driven gimbalsystem having wide servo bandwidth.

These and other objects of the invention will become more readilyunderstood upon reading of the Detailed Description of the Invention inconjunction with the drawings in which:

FIG. 1 is a three dimensional view of a preferred case-to-caseembodiment of the invention,

FIG. 2 is a view of a modification of the case-to-case preferredembodiment of FIG. 1,

FIG. 3 is a three dimensional view of another embodiment of theinvention employing a rotor-to-case configuration, and

FIG. 4 is a view of still another embodiment of the invention employinga rotor-to-rotor configuration.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 represents the preferred embodiment of the invention. Pedestal 10is fitted with motor 12. Rotor shaft 14 is fixed to pedestal 10 at hole16 by set screw 18. A dummy shaft 15 (not shown) may be journaledbetween motor 12 and pedestal 10 by means of a bearing or the motorrotor may employ a double ended shaft. Since shaft 14 is fixed topedestal 10, shaft 14 cannot rotate with respect to pedestal 10. Whenmotor 12 is energized, case 20 of motor 10 rotates as shown at arrows22. Motor 24 has case 26 which is fixed to case 20 of motor 12, forexample, by means of welding 28. Alternatively, the two motor cases maybe fabricated as a single part. Rotor shaft 30 of motor 24 is fixed toplatform support 32. Platform support 34 is connected to motor 12 case20 by means of dummy shaft 36 and idler bearing 38. Dummy shaft 36 andmotor 24 rotor shaft 30 share common axis 39. When motor 24 isenergized, shaft 30 rotates as shown at arrows 40. Since shaft 30 isfixed to platform support 32 by a set screw or other means (not shown),support 32 rotates about axis 39 with shaft 30 and drives platform 42which is fixed to supports 32, 34. The configuration as describedprovides for non-symmetrical mounting of platform 42 on supports 32 and34. This allows space for mounting, for example, gyroscope 44 on theunderside of platform 42. While the axes of motor 12 and motor 24 arepreferably orthogonal, it is not necessary to the operation of theinvention and in some applications the axes may not be orthogonal.

An alternative preferred embodiment of the invention is illustrated inFIG. 2. Motor 12 is basically the same as that of FIG. 1. The functionof motor 24 of FIG. 1 is accomplished by motors 50 and 52 which havetheir cases fixed to case 20 of motor 12. Alternatively, either ofmotors 50, 52 may be a dummy unit having an internally or externallyjournaled shaft for free rotation. Mounts 32 and 34 are the same andserve the same function as those identically referenced items in FIG. 1.The configuration of FIG. 2 provides a symmetrical mount for platform 54which may be a mount for a sensor such an an antenna or optical device.The pedestal for motor 12 of FIG. 2 is not shown for clarity but wouldbe similar to or identical with that of pedestal 10 of FIG. 1. Theconfigurations of the invention disclosed in FIGS. 1 and 2 may bereferred to as "case-to-case" configurations since the cases of thedrive motors are each fixed to another.

FIG. 3 shows another embodiment of the invention which illustrates a"shaft-to-case" or "rotor-to-case" configuration. Case 62 of motor 60 isfixed to pedestal 64. Frame 66 is disposed about motor 60 and is fixedto rotor shaft 68 of motor 60 in two places; i.e., motor 60 has doubleended rotor shaft 68. Frame 66 is also fixed to motor 70 case 72, asshown. Frame 78 is fixed to rotor shaft 74 of motor 70 and is journaledto dummy shaft 76, which may be a part of frame 66. Frame 78 may be apart of or be used to mount a sensor such as antenna or optical device79.

The configuration of FIG. 3 may be adapted to a "case-to-shaft"configuration (not shown) wherein case 62 of motor 60 mounts sensor 79and frame 78 becomes the equivalent of a pedestal for the system.

Another of the configuration combinations, a "shaft-to-shaft"arrangement, is illustrated in FIG. 4. Motor 80 has case 82 fixed topedestal or base 84. Frame 86 surrounds motor 80 and is fixed to motor89 drive shaft 88 in at least one place. Frame 86 also extends and isfastened to rotor shaft 90 of motor 92. Motor 92 case 94 is connected toplatform 96 for carrying or mounting an antenna or optical device.

In each of FIGS. 1, 2 and 3 the two motor axes are in a single plane.FIG. 4 shows the axes which are not in a single plane. It will beobvious that any of the configurations of FIGS. 1, 2, 3 or 4 may or maynot have motor axes in a single plane.

In operation, each of all configurations of the invention are alike inthat at least one drive motor is mounted on a first axis and at leastone other drive motor is mounted on a second axis. The axes may or maynot be coplanar or orthogonal, but they may not be parallel. The firstdrive motor(s) operates to rotate the system about the first axis andthe second drive motor(s) operate to drive the system about the secondaxis. All motors are mounted within or very close to the swept volume ofthe platform. This keeps the assembly of the invention within a verycompact total volume and positions all moving parts very close to theaxes of rotation for minimum inertial effect. This, in turn, providesvery good response time and/or may be used to reduce torque requirementsfor the system.

Each of the configurations shown allow for direct motor drive, thuseliminating many drive elements which might introduce backlash or freeplay problems or elastic effects which may reduce effective systembandwidth.

While the invention has been particularly shown and described withreference to a preferred and other embodiments thereof, it will beunderstood by those skilled in the art that various other modificationsand changes may be made to the present invention from the principles ofthe invention described above without departing from the spirit andscope thereof, as encompassed in the accompanying claims. Therefore, itis intended in the appended claims to cover all such equivalentvariations as come within the scope of the invention as described.

What is claimed is:
 1. Gimbal apparatus having at least a first and asecond gimbal axis for allowing mechanical freedom for a platform andfor driving the platform to a desired direction with respect to apedestal, the apparatus comprising:a first drive motor having a case anda rotor, said case and said rotor of said first drive motor having afirst common axis, one of said case and said rotor of said first drivemotor being fixed to the pedestal, the other of said case and said rotorof said first drive motor being a first rotatable member with respect tosaid one of said case and said rotor of said first drive motor, saidfirst rotatable member providing a rotatable output from said firstdrive motor; and a second drive motor having a case and a rotor, saidcase and said rotor of said second drive motor having a second commonaxis, said second common axis of said case and said rotor of said seconddrive motor and said first common axis of said case and said rotor ofsaid first drive motor having an angle greater than zero therebetween,one of said case and said rotor of said second drive motor being fixedto said first rotatable member, the other of said case and said rotor ofsaid second drive motor being a second rotatable member with respect tosaid one of said case and said rotor of said second drive motor, saidsecond rotatable member providing a rotatable output from said seconddrive motor, said second rotatable member being fixed to the platform,said first and second common axes having essentially a point ofintersection therebetween, said point of intersection lying within oneof said first and second drive motors and said first and second commonaxes being respectively common with the first gimbal axis and the secondgimbal axis.
 2. The apparatus according to claim 1 wherein said pedestalcomprises at least one supporting member and said one of said case andsaid rotor is fixed to said supporting member.
 3. The apparatusaccording to claim 1 wherein said pedestal comprises at least twosupporting members and said one of said case and said rotor is fixed toat least one of said two supporting members.
 4. The apparatus accordingto claim 3 wherein at least said first drive motor is located betweensaid at least two support members.
 5. The apparatus according to claim1, 2, 3 or 4 wherein said angle between said axes is essentially ninetydegrees.